RU2392648C1 - Optical scanning device and image formation device using such analyser - Google Patents

Abstract

FIELD: physics, optics.

SUBSTANCE: invention relates to optical scanning and image formation devices used in laser printing devices, copying machines etc. The device has an optical deflector and an optical image formation system. A light beam falls on the surface of the optical deflector at an angle to the optical axis of the image formation system in the main scanning plane. Between the deflector and the scanning surface there is a transmission-type image forming optical element and a reflection-type optical element which make up the optical image formation system. In the sub-scanning plane, the angle θ between the principal ray of the light beam reflected by the reflection-type optical element and the normal to the reflection-type optical element satisfies the condition θ≤45°. In the sub-scanning plane, the transmission-type optical element is placed such that interference with the transmission path of light reflected by the reflection-type optical element is avoided.

EFFECT: smaller size of the device.

14 cl, 14 dwg

Description

FIELD OF THE INVENTION

The present invention relates to an optical scanning apparatus and an image forming apparatus using such an analyzer. The present invention is preferably used in an image forming apparatus such as a laser printing apparatus (laser printer) (LBP), a digital copying machine or a multifunction printing apparatus comprising an electrophotographic process.

Various technical proposals are known for color imaging devices, which include a plurality of optical scanning devices, each of which comprises light source means, a deflecting means and an optical imaging system, and in which light beams of the plurality of optical scanning devices are respectively directed to the plurality of image carriers elements corresponding to these beams to obtain a color image.

Below, with reference to FIGS. 12-14, the basic structure and optical function of the color image forming apparatus as a comparative example are explained.

The color image forming apparatus (FIG. 12) contains independent image-bearing elements (hereinafter “photosensitive drums”) 20 corresponding to the colors “yellow”, “magenta”, “cyan” and “black”. Each photosensitive drum 20 contains an electrical conductive element with a photosensitive layer deposited on it. An electrostatic latent (latent) image is formed by a light beam (laser beam) from an optical scanning device.

The optical scanning device 21 (Fig. 12) (scanning optical device) is designed to project a light beam based on the information related to the image applied to it from the image reading device or personal computer.

The developing device 22 is designed to form a toner image on the photosensitive drum using triboelectrically charged toner particles, and the intermediate transport tape 23 is used to transfer the toner image existing on the photosensitive drum to a sheet of paper.

The paper cassette 24 is intended for storing sheets of paper on which toner images are to be formed, a fuser fixing device 25 for thermally fixing a toner image transferred onto a sheet of paper on a paper sheet.

An image transfer paper sheet with a toner image fixed thereon is loaded onto the paper storage tray 26. The cleaning device 27 is designed to clean the toner particles remaining on the photosensitive drum.

To form an image, a light beam emitted by a laser based on image-related information from an optical scanning device is projected onto a photosensitive drum, whereby an electrostatic latent image is formed on the photosensitive drum, charged by a charging device.

Subsequently, the toner particles, being triboelectrically charged inside the developing device 22, adhere to the electrostatic latent image, whereby a toner image is formed on the photosensitive drum.

The toner image is then transferred from the photosensitive drum to the intermediate transport tape and subsequently it is transferred again to the sheet of paper fed from the paper cassette installed in the lower part of the main unit, whereby the image is formed on the paper sheet.

The toner corresponding to the image thus transferred onto the sheet of paper is fixed by the fixing device 25, and the sheet of paper is unloaded onto the paper storage tray 26.

FIG. 13 is a side view of a sub-scan showing the image forming station of FIG. 12. The imaging station consists of two optical scanning devices SR and SL. Since these two optical scanning devices SR and SL have a lateral symmetrical structure with respect to the optical deflector 28, digital reference numbers are shown for only one of them (optical scanning devices SR), and a description is provided for only one device.

The optical scanning device comprises a rotatable polygonal mirror 28 (hereinafter, also referred to as a "polygonal mirror"), so as to deflect a light beam (laser beam) emitted from the image-related base and two f-θ 29 and 30 lenses for scanning during scanning with a constant speed of the light beam and its image on a photosensitive drum in the form of a spot.

Then, a light beam transmitted through the f-θ 29 and 30 lenses moves through a plurality of reflective mirrors 31a-31d to reflect light in a predetermined direction and passes through a dustproof glass 32 to protect the optical scanning device from dust.

Then, an electrostatic latent image is formed on the surface of the photosensitive drum by means of a light beam passing through the dustproof glass 32.

In optical scanning devices of this type, in order to comply with the tendency to ensure the small size of the image forming apparatus, a method was adopted for scanning and exhibiting four photosensitive drums using one polygon mirror drive unit (Fig. 13).

This method uses two optical scanning devices SR and SL to project a plurality of light beams in the direction of opposing surfaces of the polygon mirror 28, respectively.

Each SR or SL device projects two light beams mutually offset in parallel by a predetermined distance in the vertical direction onto the deflecting surface (reflection surface) of the polygonal mirror 28 to perform deflecting scanning.

There are two lens blocks f-θ 29 and 30 to depict the light beams of the upper and lower light paths on the photosensitive drums, respectively.

Each of these two lenses f-θ 29 and 30 has the same lens surface at two vertical levels, i.e. on the upper and lower surfaces. The f-θ lens can be made by gluing two lens parts, or it can be performed by hollow molding in the form of a molded lens.

In an optical scanning device having two vertical levels, as described above, it is necessary to use a deflecting surface in order to deflect light beams to the upper and lower light paths during scanning, respectively. Thus, a polygonal mirror of large thickness or a polygonal mirror having a two-level structure was used.

Such a design should have a significant engine load, which drives a large polygonal mirror.

In contrast, FIG. 14 shows a color image forming apparatus in which a polygon mirror of smaller thickness.

14, the imaging station consists of two optical scanning devices SR and SL. Since these two optical scanning devices SR and SL have a symmetrical structure with respect to the optical deflector 33, reference numbers are indicated for only one of them (optical scanning devices SR), and a description is provided for only one device.

In this case, the polygonal mirror 33 is made thinner, which ensures the incidence of light beams on the deflecting surfaces 33a of the polygonal mirror 33 at different angles (oblique incidence) in the sub-scan plane (optical system with oblique incidence of the beam).

After the light beams during scanning are deflected by the polygonal mirror 33, some pass through two common lenses f-θ 35 and 36.

Then one (U) of the light beams passing through the f-θ 35 and 36 lenses is directed to the photosensitive drum 38a using two reflecting mirrors 34a and 34c and one concave mirror 34b. In addition, the second (L) of light beams passing through the f-θ lenses 35 and 36 is directed to the photosensitive drum 38b using two reflective mirrors 34d and 34f and one concave mirror 34e.

On Fig separation of the paths of light beams is performed using a reflective mirror 34d, which is located in the middle of the light path.

More specifically, the light beam L, which scans the lower part, is reflected upward by the reflecting mirror 34d so that it intersects with the light beam U, which scans the upper part. Then, the light beam L is directed to the photosensitive drum 38b through a plurality of reflective mirrors 34c and 34f, which are located in the upper part of the optical system unit.

A plurality of reflective mirrors are used to direct a plurality of light beams to the corresponding surfaces of the photosensitive drums (Fig. 14), see, for example:

Japanese Patent Application Laid-Open No. 2004-21133 (D1);

Japanese Patent Application Laid-Open No. 2000-231074 (D2);

Japanese Patent Application Laid-Open No. 2005-338573 (D3);

Japanese Patent Application Laid-Open No. 7-287180 (D4);

Japanese Patent Application Laid-Open No. 62-267419 (D5);

Japanese Patent Application Laid-Open No. 2004-317790 (D6).

The color image forming apparatus, which has been described above as a comparative example, has many disadvantages as indicated below.

The first problem is that a huge number of reflective mirrors are required to direct the light beam to the photosensitive drum.

For example, in FIG. 13, three reflective mirrors 31b, 31c and 31d are used generally throughout the same light path. In addition, FIG. 14 also uses three reflective mirrors 34a, 34b and 34c (34d, 34e and 34f) along the same path.

This increases the complexity of the device due to the increased number of individual components, and also leads to the need to increase the space for placing mirrors. This causes an increase in the size of the entire system.

In contrast, Patent Document D1 proposes a method for reducing the height of an optical scanning device in the sub-scanning direction and for reducing the number of reflective mirrors.

In this approach, light transmission paths are specially developed and, when the size of the image forming lenses is taken into account, the light transmission paths are enlarged to bypass the image forming lens.

In addition, Patent Document D3 proposes a method for reducing the height of an optical scanning device in a sub-scanning direction. In D3, attempts are made to reduce the height of the device depending on the angle of reflection of the reflecting mirror, the distance from the imaging lens to the reflecting mirror, and the height of the imaging lens. It is specifically indicated that by limiting the height of the imaging lens to 6-10 mm, the reflection angle for the light path can be reduced.

However, if the height of the imaging lens is reduced in the case of a lens made of resin (“resin lens”), which was commonly used for the imaging lens, the following problems will arise.

In a resin lens formed using a mold, if the height of the lens relative to the thickness of the lens is reduced along the optical axis, the cooling process after removing the lens from the mold occurs from the upper and lower parts of the lens.

As a result, the distribution of the refractive index and the distribution of birefringence within the subscan section (direction along the height of the lens) are easily formed inside the lens.

As a result, the performance of the display generation in the sub-scanning direction is significantly increased. Therefore, it is actually difficult to reduce the height of the lens, as proposed in patent document D3.

In addition, in an oblique incidence optical system (Fig. 14), there is another problem: due to oblique incidence of the light beam on the f-θ lens (imaging lens) in the sub-scanning plane, the aberration worsens and the performance of obtaining a point (as a spot) image is worsened . In addition, the scanning path is curved on the scanning surface.

In contrast, in Patent Document D6, as shown in FIG. 10, illustrating a third embodiment of the claimed invention, the optical power distribution of the f-θ lens of the two-part structure in the sub-scanning direction is concentrated on the second f-θ lens, and the second f-θ lens is offset in the sub-scan plane relative to the light beam.

This configuration leads to a decrease in aberration and a decrease in the magnitude of the bend of the scanning path.

With respect to determining the light path (FIG. 13), the light path increases to surround the lenses.

In patent documents D4 and D5, similarly to D6, in the sub-scan plane, part of the f-θ lenses is offset relative to the light beam.

These structures are intended to avoid a surface image caused by a false image forming an image of the lens, and it is assumed that all image forming lenses to be displaced have a curvature in the sub-scanning direction, as well as optical power.

Patent documents D4 and D5 do not disclose approaches to reduce the size of the complete system.

Patent Document D2 discloses an example in which the imaging lens is tilted approximately 1 to 4 degrees to prevent a false image, and an example in which, after directing the scanning light beam through the imaging lens twice, the light beam falls obliquely within the plane sub-scans to share the light path.

Then, similarly to D6, an attempt is made to determine the angle of reflection of the cylindrical mirror in order to reduce the deterioration of the operating characteristics of the formation of a point image and the bending of the scanning path due to oblique incidence.

However, patent document D2 does not fully discuss the increase in the light path to reduce the size of the entire system.

SUMMARY OF THE INVENTION

The present invention is directed to a compact optical scanning device by which an increase in the light transmission path is provided, and the height in the sub-scanning direction can be reduced, as well as to an image forming apparatus using such an optical scanning device.

In accordance with one aspect of the present invention, there is provided an optical scanning device, comprising: an optical deflector configured to scan to deflect a light beam emitted from a light source; and an optical imaging system configured to create an image of the light beam when scanning a deflected deflecting surface of said optical deflector;

wherein the light beam incident on the deflecting surface of the optical deflector is incident perpendicular to the deflecting surface in the sub-scan plane, the light beam incident on the deflecting surface of the optical deflector is incident at an angle relative to the optical axis of the imaging optical system in the main scanning plane, while along light paths between the optical deflector and the scanning surface are placed imaging optical element through passage a constituting the optical imaging system and the optical element of the reflective type, which are placed in the indicated order from the optical deflector, and in the sub-scanning plane, the angle defined between the main beam of the light beam reflected by the optical element of the reflective type and the normal to the optical element of the reflective type is indicated through θ, the condition θ≤45 degrees is satisfied, and at the same time, in the sub-scan plane, the image-forming optical element of the through type is located k, in order to avoid interference with the transmission of light reflected by an optical element of a reflective type, the center line of the path of an imaging optical element of a pass-through type is positioned on one side of the main beam of a light beam incident on an image-forming optical element of a pass-through type whose side is away from the light path, reflected by the optical element of the reflective type.

If the angle defined in the sub-scanning plane between the main beam of the light beam reflected by the optical element of the reflective type and the normal to the optical element of the reflective type is denoted by θ, the condition θ≤30 degrees can be satisfied.

If the optical power of the through-type imaging optical element in the sub-scan plane is denoted by φ _i and the optical power of the optical imaging system in the sub-scan plane is denoted by φ _all , the condition | φ _i ≤φ _all | ≤0.01 can be satisfied.

If the radius of curvature in the sub-scanning direction of the light exit surface of the imaging optical element of the through type is indicated by R1 (mm) and the radius of curvature in the sub-scanning direction of the light exit surface of the imaging optical element of the through type is designated R1 (mm), the condition | 1 / R1 | + | 1 / R2 | <0.0067 (1 / mm).

In the subscan plane, the optical axis of the imaging optical element of the pass-through type may not coincide with the center line of the imaging optical element of the pass-through type, and in the plane of the subscan, the main beam of the light beam incident on the imaging optical element of the pass-through type can pass through the optical axis of the imaging optical element of passage type.

The imaging optical element of the passage type can be made of resin material.

If in the sub-scan plane the height of the external outline of the mounting frame holding the image-forming optical element of a passage type is indicated by H (mm) and the physical distance from the center line of the contour to the main beam of the light beam incident on the light input surface of the image-forming optical element of the passage type is indicated through dZ (mm), the condition 0.05 <dZ / H <0.5 can be satisfied.

The image-forming optical element of a through type may have a base surface for positioning in the plane of the main scan, and the base surface may be located outside the effective region of the optical surface of the image-forming optical element of a through type.

The imaging optical element of a through type may have a support protrusion for determining the base position in the plane of the main scan, and the protrusion can be located on the side of the surface of the light input for imaging an optical element of a through type.

In the sub-scanning plane, the image-forming optical element of a through type may have a concave support element for determining a basic position in the plane of the main scan, and the supporting element can be located on the side of the outer circumferential part of the image-forming optical element in a through type in the sub-scanning direction.

In the sub-scan plane, the end surface on the outer circumference of the mounting frame in the sub-scan direction for holding the imaging optical element of the through type may have a cone-shaped geometry along the light path reflected by the optical element of the reflective type.

In accordance with another aspect of the present invention, there is provided an optical scanning apparatus comprising two optical imaging systems, as set forth above, and disposed in a sub-scanning plane to accommodate an optical deflector between them.

In accordance with a further aspect of the present invention, there is provided an image forming apparatus, comprising: an optical scanning apparatus; a photosensitive element located on the scanning surface; a developing device configured to develop into the toner image an electrostatic latent image formed on the photosensitive member by means of a light beam scanned by the optical scanning device; a transfer device configured to transfer the developed toner image onto the transfer material; and a fixing device configured to secure the transferred toner image to the transfer material.

In accordance with a further further aspect of the present invention, there is provided an image forming apparatus, comprising: an optical scanning apparatus as described above; a printer device controller, configured to convert the encoded data input into it from an external device into an image-related signal and input the image-related signal into said optical scanning device.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the present invention will become more apparent upon consideration of the following description of preferred embodiments of the present invention, with reference to the accompanying drawings, in which:

Figure 1 is a diagram of the direction of the rays in the sub-scan plane according to the first embodiment of the present invention;

Figure 2 is a diagram of the direction of the rays in the plane of the main scan according to the first embodiment of the present invention;

Figure 3 is a part of a diagram in a sub-scan plane according to a first embodiment of the present invention;

4 is a part of a diagram in a sub-scanning plane according to a second embodiment of the present invention;

5 is a part of a diagram in a sub-scanning plane according to a third embodiment of the present invention;

6 is a diagram in the plane of the main scan according to the fourth embodiment of the present invention;

7 is a diagram in the plane of the main scan according to the fifth embodiment of the present invention;

FIG. 8 is a diagram in a main scan plane according to a sixth embodiment of the present invention; FIG.

Fig. 9 is a part of a diagram in a sub-scanning plane according to a seventh embodiment of the present invention;

10 is a diagram of a main part of an image forming apparatus (sectional view) according to the invention;

11 is a diagram of a main part of a color image forming apparatus (sectional view) according to the invention;

12 is a diagram of a main part of a known image forming apparatus;

Fig. 13 is a diagram of a main part of the claimed image forming apparatus (sectional view), a comparative example;

Fig. 14 is a diagram of a main part of an image forming apparatus (sectional view), a comparative example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In the present invention, the term “optical path length” refers to the optical distance from the deflection point of the optical deflector to the surface to be scanned (scanning surface).

It should be noted that in the present invention, the words "optical distance" mean "the distance through which the light beam passes along the light path."

It should also be noted that in the present invention, the words “physical distance” mean the length of a straight line connecting the scanning surface 11 and the optical deflector 5.

Option 1 implementation

1 shows a sectional view, i.e. a sub-scan view of a main body according to a first embodiment of the present invention along a sub-scan direction. Figure 2 shows a sectional view, i.e. a plane view of the main scan of the main part according to the first embodiment of the present invention along the main scan direction. Figure 3 shows a sectional view, i.e. view in the plane of the sub-scan for the part of figure 1 in the direction of the sub-scan.

It should be noted that in the following description, the term “main scanning direction” (Y-direction) refers to the direction in which the light beam is deflected by the optical deflector during scanning.

The term "sub-scanning direction" (Z-direction) refers to a direction that is parallel to the rotational axis of the deflecting means.

The term "main scan plane" refers to a plane with respect to which the sub-scan direction (Z-direction) is perpendicular.

The term “sub-scan plane” refers to a plane with respect to which the main scan direction (Y-direction) is perpendicular.

The imaging device (Figs. 1-3) comprises two optical scanning devices SR and SL. Since these two optical scanning devices SR and SL have a lateral symmetrical structure with respect to the optical deflector 5 and the same optical function, the following description relates mainly to the optical scanning device SR.

The light source means 1 comprises a semiconductor laser. A condenser lens 2 (collimator lens) is used to convert the diverging light beam emitted from the light source means 1 into a parallel light beam.

It should be noted that the incident light beam on the condenser lens 2 is not limited to a parallel light beam, but it can be a converging light beam or a diverging light beam. Aperture diaphragm 3 limits the light beam passing through it to create the shape of the beam profile. The cylindrical lens 4 has a predetermined optical power only in the sub-scan plane (sub-scan direction). Its function is to create in the sub-scanning plane an image for the light beam passing through the aperture diaphragm 3, in the form of an image of a line (dash) on the deflecting surface (reflection surface) 51 of the deflecting means 5, which will be described below.

It should be noted that the condenser lens 2 and the cylindrical lens 4 can be made in one piece in the form of a single optical element (anamorphic lens).

In addition, elements such as a condenser lens 2, aperture diaphragm 3 and a cylindrical lens 4 are components of the input optical system LA, which ensures that the light beam from the light source means is incident on the deflecting means 5.

The optical deflector 5 as a deflecting means (polygonal mirror) has a design with six surfaces. When scanning, it deflects the light beam from the means 1 of the light source.

The optical deflector 5 is rotatably mounted, and when rotated at a constant speed in a predetermined direction by a motor (not shown), the deflector scans the scanning surface 11 in the main scanning direction.

The optical imaging system LB (f-θ lens system) in the present embodiment is composed of several (two in this example) imaging optical elements of a through type (the first and second imaging lenses 6 and 8) for directing the light beam from the optical deflector 5 to the surface 8 of the scan.

The optical imaging system LB generates from the light beam based on the information related to the image and deflected by scanning by rotating the optical deflector 5 a spot on the surface of the photosensitive drum 11 as the scanning surface, within the main scanning plane (main scanning direction).

In addition, it is used to provide an optically conjugate relationship between the deflecting surface 51 of the rotating optical deflector 5 and the surface 11 of the photosensitive drum in the sub-scan plane to compensate for the inclination of the surface.

The first and second reflecting mirrors 7 and 9 are each designed to “bend” the light path. These mirrors are located along the light path between the optical deflector 5 and the scanning surface 11.

Of the first and second reflecting mirrors 7 and 9, the first reflecting mirror 7, which is an optical element of a reflective type, which is optically closest to the optical deflector 5, is located between the first and second image forming lenses 6 and 8 (two image-forming optical elements of a through type).

The first and second reflecting mirrors 7 and 9 as optical elements of the reflective type are composed of flat mirrors that do not have optical power.

It should be noted that in the described embodiment, the word "optical" means the direction in which the light beam moves. There is also a protective glass 10 and a surface 11 of the photosensitive drum as a scanning surface.

The center line 61 represents the contour (external geometry) of the mounting frame (not shown) of the image forming optical element of the passage type, the mounting frame being configured to hold the image forming lens as an optical element.

The light beam 14 (scanning light beam) during scanning is deflected by means of the deflecting surface 51. Path 15 is the light path, if reflected by the first mirror 7. The shutter is indicated by 67.

The optical scanning device according to the invention is a scanning system with a deviation in one plane, in which scanning is performed within a plane perpendicular to the deflecting surface of the optical deflector (polygonal mirror) 5, in the sub-scan plane (FIG. 1).

Thus, the input optical system LA, protruding from the means 1 of the light source in the direction of the cylindrical lens 4, is located within the sheet of the drawing, which corresponds to the deflecting surface (Figure 2).

In addition, the light beam incident on the deflecting surface 51 of the optical deflector 5 falls at a limited angle with respect to the optical axis of the imaging system LB, within the main scan plane.

In addition, in this embodiment, as can be seen from FIG. 2, identical optical scanning devices SR and SL are located on the right and left side of the optical deflector 5, the optical deflector 5 being used together for both devices to scan multiple scanning surfaces.

The technical characteristics of the optical scanning device in the first embodiment of the present invention are shown below in Tables 1, 2 and 3.

Table 1 Angle of incidence within the deflection plane Surface R D N Light source 1 one 30.28 1,000 Condenser Lens 2 2 46.63203 1.00 1,785 3 15,51899 2.00 1,582 four -21,487 6.00 1,000 Aperture 3 5 endless 5.92 1,000 Cylindrical lens 4 6 aspherical (described below) 7.00 1,511 7 endless 83.90 1,000 Deflecting surface 5 8 endless 30.00 1,000 1st imaging lens 7 9 aspherical (described below) 7.50 1,524 10 aspherical (described below) 91.00 1,000 2nd imaging lens 9 eleven aspherical (described below) 5.50 1,524 12 aspherical (described below) 66.00 1,000 Safety glass 10 13 endless 1.80 1,511 fourteen endless 64.70 1,000 Surface 11 scan fifteen endless

table 2 Aspherical shape 6th surface 9th surface 10th surface 11th surface 12th surface Meridional form R endless -6.39 + 01 -4.17 E + 01 -1.16E + 03 1,58E + 03 K 0 -4.85E + 00 -1.30E + 00 0 -1.38E + 03 B4 0 2.89E-07 7.71E-08 0 -1.65E-07 B6 0 -2.58E-10 1,27E-10 0 1,16E-11 B8 0 -5,12E-14 -3.67E-13 0 -6.82E-16 B10 0 9.72E-17 1,58E-16 0 7.98E-20 Sagittal form r 44.88 -1.00E + 03 -1.00E + 03 -1.00E + 03 -3.33E + 01 D2 0 0 0 0 4.77E-05 D4 0 0 0 0 -6.42E-09 D6 0 0 0 0 6,48E-13 D8 0 0 0 0 -3.28E-17 D10 0 0 0 0 5,15E-22

The circumscribed circle of the polygonal mirror = φ40.

The number of deflecting surfaces of the polygonal mirror = 6.

The angle defined between the optical axes of the input optical system and the optical imaging system = 70 degrees;

The reflecting point of a polygonal mirror for a light beam in the center of the image with respect to the center (0,0) of the polygonal mirror = (15.05, 8.71).

The distance between the center of the polygonal mirror and the reflecting mirror = 85.

The angle of incidence, determined between the normal to the first reflecting mirror and the incident light beam = 7.3 degrees.

The distance from the first reflecting mirror to the second reflecting mirror = 140.

The angle of incidence, determined between the normal to the second reflecting mirror 9 and the incident light beam = 62.3 degrees.

Table 3 Fθm 227.1 Fθs 65,4 G1m 205.6 G1s 740116 G2m -1276.9 G2s 65.6 TC 266.5 φa11 0.01529 φ1 1,4E-06 φ2 0.01525 φ1 / φall 8,8E-05 | 1 / r1 | + | 1 / r2 | 2,0E-03

Moreover, the expression is determined as described below.

The lens shape (toric shape) contains an aspherical shape, which can be expressed by a function of up to the tenth order with respect to the direction of the main scan. Where the intersection point with the optical axis is taken as the origin, the direction of the optical axis is taken as the X axis, the axis in the main scan plane and orthogonal with respect to the optical axis is taken as the Y axis, and the axis in the sub-scan plane and orthogonal with respect to to the optical axis is taken as the Z axis, the meridional direction corresponding to the main scan direction is expressed according to

where R is the radius of curvature and K, B ₄ , B ₆ , B ₈ and B ₁₀ are aspherical coefficients.

The sagittal direction corresponding to the sub-scanning direction (the direction including the optical axis and orthogonal with respect to the main scanning direction) is expressed by the equation

where r '= r0 (1 + D ₂ Y ² + D ₄ Y ⁴ + D ₆ Y ⁶ + D ₈ Y ⁸ + D ₁₀ Y ¹⁰ ), r0 is the radius of the sagittal curvature on the optical axis; D ₂ , D ₄ , D ₆ , D ₈ and D ₁₀ are coefficients.

In addition, in the tables:

G1m is the focal length of the first imaging lens in the main scanning direction;

G2m is the focal length of the second imaging lens in the main scanning direction;

fθm is the combined focal length of the first imaging lens and the second imaging lens in the main scanning direction;

G1s is the focal length of the first imaging lens in the sub-scanning direction; φ is the optical power;

G2s is the focal length of the second imaging lens in the sub-scanning direction; φ2 is the optical power.

fθs is the combined focal length of the first imaging lens and the second imaging lens in the sub-scanning direction; φ _all is the optical power;

TC is the distance from the polygonal mirror to the scanning surface.

In addition, in the tables, the symbol “eX” means “x10 ^-x ”.

In the present embodiment, the diverging light beam emitted from the semiconductor laser 1 is converted into a parallel light beam by means of a condenser lens 2. Then the light beam (light flux) is limited to the aperture diaphragm 3, and after that it falls on the cylindrical lens 4.

Inside the plane of the main scan, the light beam incident on the cylindrical lens 4 leaves it without being changed and falls on the deflecting surface 51 of the optical deflector 5.

On the other hand, within the sub-scanning plane, the light beam is further reduced and displayed as a line image (image of a line extending in the main scanning direction) onto the deflecting surface 51 of the rotating optical deflector 5.

The light beam from the input optical system LA is incident perpendicularly to the deflecting surfaces of the optical deflector 5 in the sub-scanning plane and is focused on the deflecting surface 51.

In addition, the light beam incident on the deflecting surface 51 of the optical deflector 5 falls with a limited angle relative to the optical axis of the image forming system LB in the main scanning plane.

Then, the light beam, when scanned, deflected by the deflecting surface 51 of the optical deflector 5, passes through the first image forming lens 6; then it is reflected by the first reflecting mirror 7; then it passes through a second imaging lens 8; then it is reflected by the second reflecting mirror 9; and finally displayed as a spot on the photosensitive surface 11 of the drum.

Thus, the image is recorded on the photosensitive surface 11 of the drum as a recording medium.

The optical function of the image forming system LB, which consists of the first and second image forming lenses 6 and 8, is explained below.

In the present embodiment, the first and second imaging lenses 6 and 8 are made of resin (plastic).

The imaging system LB displays a light beam that is deflected by the optical deflector 5 during scanning onto the scanning surface 11 to form a beam spot thereon and scan the scanning surface 11 at a constant speed.

The imaging lens made of resin is manufactured using the known molding technique by filling the mold with resin and removing it from the mold after cooling.

Thus, an imaging lens can be manufactured more easily compared to a traditional imaging lens made of glass.

As indicated in Table 1, the first imaging lens 6 having optical power (refractive power of the lens) mainly in the main scanning direction has an aspherical surface geometry having the shape of a lens expressed by a function of the above equation.

In the present embodiment, the first imaging lens 6 (imaging optical element of passage type A), for which is the shortest distance between the light path 15 reflected by the first reflecting mirror 7 as an optical element of the reflective type and the outer circumference of one of the mounting frames (not shown) for the image-forming optical elements of the passage type, holding a plurality of image forming lenses, has optical power in the sub-scan direction less optical power in the direction of the main scan.

Also, the first imaging lens 6 is composed of a meniscus lens (meniscus lens) having a non-arc geometry in the plane of the main scan and having a concave surface facing the side of the optical deflector 5.

In addition, the geometry of the first imaging lens 6 in the plane of the main scan is symmetrical with respect to the optical axis.

With respect to the direction of the sub-scan, the light entrance surface and the light exit surface have no optical power and have the same curvature. However, both surfaces may have a cylindrical shape, being flat in the sub-scanning direction.

It provides an imaging function primarily in the direction of the main scan relative to the incident light beam.

The mounting frame is integrally formed with a through-type imaging optical element through a molding process. However, the mounting frame may be formed separately from the imaging optical element of the passage type.

On the other hand, the second imaging lens 8 is an anamorphic lens having optical power mainly in the sub-scanning direction, as shown in Table 1. The lens shape is the geometry of the aspherical surface, expressed by a function of the above equation.

The second imaging lens 8 has a higher optical power in the sub-scanning direction (in the sub-scanning plane) than the optical power in the main scanning direction (in the main scanning plane). Also, the light entrance surface in the plane of the main scan has an arc-shaped shape, and the other surface has a non-arc shape.

The geometry (shape) in the plane of the main scan is symmetrical with respect to the optical axis, and it has no optical power in the direction of the main scan on the axis.

As for the geometries (shapes) in the sub-scanning plane, the light entrance surface has a flat surface having extremely weak curvature, while the light exit surface has a convex shape in which the curvature changes gradually from the optical axis to the outside of the optical axis and the geometry is symmetrical with respect to the optical axis.

For a light beam incident on it, the lens has an imaging function in the sub-scanning direction and a weak distortion correction function in the main scanning direction.

Regarding the relationship of the display in the sub-scanning direction of the image forming system LB, which is composed of the first and second image forming lenses 6 and 8, it provides what can be called a surface tilt correction system in which the deflecting surface 51 and the scanning surface 7 are interconnected.

It should be noted that the optical imaging system LB does not always have to be the functional expression shown in Table 1, it can be a known expression.

In addition, it may have asymmetric geometry with respect to the optical axis to further improve the image forming performance.

In this embodiment (FIG. 3), after the light beam (scanning light beam) 14, when scanned is deflected by the deflecting surface 51, falls onto the first imaging lens 6, it is reflected by the first reflecting mirror 7.

Within the sub-scanning plane, the first imaging lens 6 is positioned so as to avoid interference with the passage of light reflected by the reflective optical element, the center line 61 of the contour of the mounting frame (not shown) of the image-forming optical element of the passage type is located on the side of the center line (main beam) a light beam incident on the first imaging lens 6, the side of which is removed from the reflected light path 15.

In this embodiment, by shifting the first imaging lens 6 in a direction perpendicular to the scanning light beam 14 and only by the physical distance (shift amount) dZ, which will be described later, it is possible to avoid interference between the reflected light path 15 and the first imaging lens 6.

Based on this, the reflection angle θ in the first reflection mirror 7 can be made small, and this contributes to a decrease in the height of the device in the sub-scanning direction.

It should be noted that, as shown in Table 1, the radius of curvature r for the first imaging lens 6 in the sub-scanning direction is 1000, and this lens is designed so that its apex is aligned with the center line 61 of the contour. In this embodiment, if the angle defined between the main beam of the light beam reflected by the first reflecting mirror 7 and the normal to the first reflecting mirror 7 is denoted by θ, the following condition is satisfied:

Expression (3) of the condition sets the reflection angle θ reflected by the first reflecting mirror 7.

If the upper limit of expression (3) is exceeded, a contribution to reducing the size of the complete system is no longer made. Those. if the reflection angle θ exceeds 45 degrees, the angle determined between the main beam of the scanning light beam 14 and the reflected light transmission path 15 becomes greater than 90 degrees, and thus, compactness in the horizontal direction will be lost.

Preferably, the reflection angle θ is set to not more than 45 degrees.

Preferably, the above condition (3) is set as follows:

In the present embodiment, as indicated in Table 1, θ = 7.3 degrees. This satisfies expression (3) as well as expression (4).

In addition, in the present embodiment, if we denote the height of the external geometry of the mounting frame of the imaging optical element of the passage type, which holds the first imaging lens 6, through H and the physical distance (shift value) from the center line 61 of the contour to the main beam of the incident light beam (scanning light beam) 14 through dZ, the condition

Expression (5) refers to the relationship between the physical distance from the center line 61 of the contour to the incident light beam 14 and the height of the contour. If expression (5) is not satisfied, it is difficult to increase the light path. It is also difficult to reduce the height of the device in the sub-scanning direction.

More preferably, expression (5) is defined as

In the described embodiment, H = 13.0 mm and dZ = 1.5 mm. Thus, dZ / H = 0.115. This satisfies expression (5) as well as expression (6).

In the described embodiment, as shown in FIG. 3, the height of the device in the sub-scanning direction can be reduced by making the angle θ small.

Moreover, the first imaging lens 6 should be shifted in a direction perpendicular to the scanning light beam 14 in order to avoid interference between the reflected light path 15 and the first imaging lens 6.

Although the effect of decreasing the height can be enhanced if the shift amount dZ is performed larger, the largest possible shift amount is 1/2 of the lens height H, and this determines the upper limit for expression (5).

In addition, in a resin lens that is molded by means of a mold, if the height of the lens is small compared to the thickness of the lens in the direction of the optical axis, during the cooling process, immediately after removing the lens from the mold, cooling starts and develops from the upper and lower parts of the lens.

As a result of this, the distribution of the refractive index and the distribution of birefringence are easily formed in the inner part of the lens within the scanning sub-plane (direction along the height of the lens). It is known that this effect becomes more significant if the distance from the central axis of the lens contour becomes larger and that the display performance deteriorates sharply from about two-thirds (2/3) of the gap from the center of the contour to the outer outer edge.

Therefore, if the imaging performance of the device is a priority, the ratio should preferably satisfy dZ / H <0.3.

The upper limit of expression (6) defines this.

The lower limit of expressions (5) and (6) defines the definition of the lower limit of the magnitude of the shift of the first imaging lens 6.

If the shift amount is small, the effect of preventing interference with respect to the interference between the reflected light path 15 and the first imaging lens 6 becomes insufficient, and interference will occur if the position of the reflected light path 15 or the position of the first imaging lens 6 is changed due to a tolerance during assembly.

In an embodiment, as described above, the optical power of the first imaging lens 6 in the sub-scanning direction is less than the optical power in the main scanning direction.

Here, the width of the light beam for the light beam reflected by the first reflecting mirror 7 is taken as La, and the distance from the first imaging lens 6 to the first reflecting mirror 7 is taken as L.

In addition, the angle of reflection between the main beam of the light beam reflected by the first reflecting mirror 7 and the normal to the first reflecting mirror 7 is taken as G, and the height of the contour of the mounting frame of the image-forming optical element of the passage type is taken as H.

The shift amount dZ of the first imaging lens 6 should preferably satisfy the following condition:

Expression (7) is a condition for setting the shift value dZ of the first imaging lens 6.

If expression (7) is not satisfied, the effect of preventing interference with respect to interference between the reflected light path 15 and the first imaging lens 6 becomes insufficient, similar to expression (5), and interference will occur if during assembly the position of the reflected light path 15 or the position of the first imaging lens 6 changes due to tolerance.

In this embodiment, if the optical power of the first imaging lens 6 (imaging optical element C of the pass-through type) in the sub-scanning plane is indicated by φ _i and the optical power of the imaging system LB in the sub-scanning plane is indicated by φ _all , the condition is satisfied

Expression (1) is a condition for setting the ratio between the optical power of the image forming lens 6 in the sub-scanning direction (1 / "focal length") forming the image forming system LB and the optical power (1 / "focal length") of the image forming system.

Expression (1) indicates the condition that the ratio of the optical power of the first imaging lens 6 should be less than the specified value.

If the optical power ratio of the first imaging lens 6 is greater than the upper limit of expression (1), the aberration will deteriorate when the optical power ratio of the first imaging lens 6 is displaced parallel to the optical axis, as described above, so that light spot diameter damage and bending will occur scanning paths (scanning beam).

In this embodiment, as shown in Table 1, there is a relation

This satisfies expression (1).

More preferably, expression (1) is set as follows:

In addition, in this embodiment, if the radius of curvature of the first imaging lens 6 on the side of the optical deflector and the side of the scanning surface is indicated by R1 and R2, respectively, the following condition is satisfied

Expression (2) is a condition for specifying the curvature of the first imaging lens 6 constituting the imaging optical system LB in the sub-scanning direction.

Expression (2) specifies that the curvature values for the light entrance surface and the light exit surface of the first imaging lens 6 in the sub-scanning direction are set less than a predetermined value.

If the curvature of the light entrance surface and the light exit surface of the first imaging lens 6 in the sub-scanning direction becomes much higher than the upper limit from expression (2), the aberration will deteriorate when the optical power ratio of the first imaging lens 6 is displaced in parallel with respect to the optical axis, as described above, so that there will be a deterioration in the diameter of the light spot and bending of the scanning path.

The light entrance surface and the light exit surface constitute the optical surface (lens surface).

In the present embodiment, as shown in Table 1, there is a relation

This satisfies expression (2).

More preferably, expression (2) is set as follows:

A feature of the present embodiment is that, as described above, for the imaging lenses constituting the imaging optical system LB, the first imaging lens 6 has a very small optical power in the sub-scanning direction, is shifted in the sub-scanning plane with respect to the scanning light beam 14.

It should be noted that the optical power of the first imaging lens 6 in the sub-scanning direction may be zero (not have optical power).

In addition, the curvature of the first imaging lens 6 is very small (weak), as described above. Therefore, even if it is shifted in the sub-scanning plane, the Fresnel reflected light that occurs on the surface of the lens of the first imaging lens 6 is returned to the optical deflector 5.

With this in mind, in the present embodiment, a sufficient distance is provided between the optical deflector 5 and the first imaging lens 6 and, in addition, the thickness of the optical deflector 5 in the height direction is maintained up to 2 mm or less. Thus, the structure is configured in order to avoid the negative influence of Fresnel reflected light, which otherwise could cause spurious illumination and repeated image.

In addition, a coating may be provided on the surface of the lens for the first imaging lens 6. On the other hand, in the present embodiment, as described above, with respect to the first and second imaging lenses 6 and 8, the first imaging lens 6 (imaging optical element C through passage type), which has the smallest optical power or zero optical power in the sub-scanning direction, is offset in the sub-scanning plane relative to the scanning light beam 14.

In this configuration, the negative effects on worsening aberration and bending of the scanning path are reduced.

In this embodiment, the first imaging lens 6 is offset in the sub-scanning direction by a physical distance dZ = 1.5 mm, whereby the departure of the bend of the scanning path is weakened to approximately 1 μm or less, which is a level that can be ignored.

In addition, in the present embodiment, as described above, it is ensured that the first reflective mirror 7 is located in the light path between the first imaging lens 6 and the second imaging lens 8.

In this configuration, the size of the system can be small both in the horizontal direction and in the vertical direction.

If, as the reflective type optical element, the first reflective mirror 7 is placed after the second imaging lens 8, the horizontal width becomes large.

In addition, if the first reflective mirror 7 as the reflective type optical element is placed on the optical path between the first imaging lens 6 and the optical deflector 5, the size in the vertical direction cannot be made small, although the size in the horizontal direction can be made small.

Therefore, in order to reduce the size in both directions, both horizontal and vertical, the first reflecting mirror 7 should preferably be placed in the light path between the first imaging lens 6 and the second imaging lens 8.

In this embodiment (FIG. 1), optical scanning devices SR and SL having the same structure are provided on the right and left optical deflector 5 symmetrically with respect to the plane, including the axis of rotation of the optical deflector 5, and the optical deflector 5 is used to scan a plurality of scanning surfaces.

However, the reflection angle of the second reflecting mirror 9 differs between the optical scanning devices SR and SL (FIG. 1).

The angle of reflection of the second reflecting mirror 9 can be set appropriately in accordance with the arrangement of the components of the image forming apparatus.

In the present embodiment, as described above, interference between the light beam reflected by the first reflection mirror 7 and the first imaging lens 6 can be avoided. Therefore, the number of reflection mirrors to be used can be reduced, and a compact design of the optical scanning device is achieved. .

Furthermore, since in this embodiment, the optical power of the first imaging lens 6 in the sub-scanning direction, which is the lens to be biased, is weak, the aberration deterioration due to the shift can be suppressed, and a good stain imaging condition can be maintained.

In addition, in this embodiment, in both of the left-side and right-side imaging optical systems LB (FIG. 2), the shutter elements (shutters) 67 for the first imaging lenses 6 are arranged in the same direction.

By positioning the shutter members 67 in this manner, the same components can be used for the left and right sides of the imaging lenses 6 and 8.

It should be noted that in this embodiment, a light source means (multipath light source) with a plurality of light emitting elements (light emitting points) can be used.

Option 2 implementation

Figure 4 shows a view in the plane of subscanning the main part according to the second variant implementation of the present invention.

The second embodiment differs from the first embodiment in that the end surface 62 on the outer circumferential part of the mounting frame of the image-forming optical element of the passage type holding the first image-forming lens 6 is cone-shaped, extending along the light passage 15.

Other structures and optical functions are similar to the first embodiment, and based on this, similar technical effects are achievable.

More specifically, in this embodiment, by forming an end surface (inclined portion) 62 on an outer circumferential portion of a mounting frame (not shown) of an image-forming optical element of a pass-through type, which holds the first image-forming lens 6 of a conical shape extending along the light passage 15, provides a reduction in the height of the device in the direction of sub-scanning.

Typically, for resin lenses to be molded using a mold, a release cone is provided on the outer circumference of the lens that is parallel to the direction of the optical axis of the lens, so as to reduce deformation when the lens is released from the mold.

In this embodiment, the direction of inclination of the release cone extends along the path 15 for the passage of light reflected by the first reflecting mirror 7 as an optical element of a reflective type.

In this configuration, interference between the first imaging lens 6 and the light transmission path 15 reflected by the first reflection mirror 7 can be avoided, so that the reflection angle θ of the first reflection mirror 7 can be much smaller, and the reduction in height of the device in the sub-scanning direction is further improved.

Option 3 implementation

Figure 5 shows a view in the plane of the main scan for the main part according to the third variant of implementation of the present invention.

This embodiment differs from the first embodiment in that the first imaging lens 6 has a base surface 63 for positioning the lens within the main scan plane, and this base surface of the first imaging lens is formed outside the effective area of the lens surface.

Other structures and optical functions are similar to the first embodiment, and based on this, similar technical effects are achievable.

More specifically, in this embodiment, the base surface 63 of the first imaging lens 6 for positioning the lens in the main scanning plane is performed for the first imaging lens outside the effective area of the lens surface, and further, the base surface 63 has a footprint 12 as a reference position.

The seat 12 is located outside the effective portion of the first imaging lens 6 in the main scanning direction.

In addition, the footprint 12 is performed on the frame element (not shown) and is used as the basis for the position reference in the main scanning direction for the first imaging lens 6.

Typically, the positional basis with respect to the direction of the main scan is provided above and below the central part of the first imaging lens 6 in the scanning direction of FIG. 1, for example. However, if the positional basis is provided above and below the center of the first imaging lens 6 in the scanning direction, this interferes with the path 15 of the passage of light reflected by the first reflecting mirror 7.

With this in mind, in this embodiment, a base surface 63 for positioning the lens in the main scanning plane is provided for the first imaging lens 6 outside the effective area of the lens surface. Due to this, the disadvantages described above can be eliminated.

Option 4 implementation

Figure 6 shows a view in the plane of the main scan for the main part according to the fourth embodiment of the present invention.

The present embodiment differs from the aforementioned first embodiment in that the positioning pin 64 for positioning the lens in the main scanning plane is placed outside the effective area of the lens surface for the first imaging lens 6.

The remaining structures and optical functions are similar to the first embodiment, and based on this, similar technical effects are achievable.

More specifically, in this embodiment, a locating pin 64, which acts as a positional basis for positioning the lens in the main scanning plane, is positioned for the first imaging lens 6 outside the effective surface area of the lens.

The mounting pin 64 is configured to fit snugly into the base hole of a chassis member (not shown). In addition, as can be seen from Fig.6, the installation pin 64 is placed outside the effective part of the first imaging lens 6 in the main scanning direction and provides a positional basis for the first imaging lens 6 relative to the main scanning direction.

Typically, the positional basis with respect to the direction of the main scan is provided above and below the center of the first imaging lens 6 in the scanning direction of FIG. 1. However, if the positional basis is provided above and below the center of the first imaging lens 6 in the scanning direction, it interferes with the path 15 of the passage of light reflected by the first reflecting mirror 7.

With this in mind, in this embodiment, a locating pin 64 for positioning the lens in the main scanning plane is arranged for the first imaging lens 6 outside the effective area of the lens surface. Due to this, the disadvantages described above can be eliminated.

Option 5 implementation

7 shows a view in the plane of the main scan for the main part according to the fifth embodiment of the present invention.

The present embodiment differs from the first embodiment in that the support protrusion 65 for determining the base position in the main scanning plane is placed on the side of the light entrance surface corresponding to the first imaging lens 6.

The remaining structures and optical functions are similar to the first embodiment, and based on this, similar technical effects are achievable.

More specifically, in this embodiment, the support protrusion 65, which defines the base position in the plane of the main scan, is placed on the side of the light entrance surface on the first imaging lens 6.

The support protrusion 65 is configured to fit into the base hole of the chassis member (not shown).

In addition, as shown in FIG. 7, the support protrusion 65 is arranged on the side of the light entrance surface on the first imaging lens 6.

Typically, a positional basis with respect to the direction of the main scan is provided above and below the center of the first imaging lens 6 in the scanning direction of FIG. 1. However, if the positional basis is provided above and below the center of the first imaging lens 6 in the scanning direction, it interferes with the path 15 of the passage of light reflected by the first reflecting mirror 7.

Furthermore, even if the support protrusion 65 is located on the side of the light exit surface, it easily interferes with the reflected light path 15.

Bearing this in mind, in this embodiment, the support protrusion 65, which defines the base position of the lens in the main scanning plane, is provided on the light entry side of the first imaging lens 6. Due to this, the disadvantages described above can be eliminated.

Option 6 implementation

On Fig shows a view in the plane of the sub-scan for the main part according to the sixth embodiment of the present invention.

The present embodiment differs from the first embodiment in that it comprises a concave-shaped support member 66 for determining a reference position in the main scan plane on the outer circumference of the first imaging lens 6.

Other structures and optical functions are similar to the first embodiment, and based on this, similar technical effects are achievable.

More specifically, in this embodiment, the concave-shaped support member 66, which defines the base position in the main scan plane, is located on the outer circumference of the first imaging lens 6.

The base hole (recess) 66 is configured to accommodate the mounting pin 13 of the frame element.

Typically, the positional basis with respect to the direction of the main scan is provided above and below the center of the first imaging lens 6 in the scanning direction of FIG. 1. However, if the positional basis is provided above and below the center of the first imaging lens 6 in the scanning direction, it interferes with the path 15 of the passage of light reflected by the first reflecting mirror 7.

Taking this into account, in this embodiment, the concave-shaped support member 66, which defines the lens baseline position in the main scan plane, is located on the outer peripheral part of the first imaging lens 6. Due to this, the disadvantages described above can be eliminated.

Option 7 implementation

On Fig shows a view in the plane of the sub-scan for the main part according to the seventh variant of implementation of the present invention.

The present embodiment differs from the aforementioned first embodiment in that the second imaging lens 8 (hereinafter also referred to as the “imaging optical element B is of the pass-through type”), the distance for which is between the light path 15 reflected by the first reflecting mirror 7 and the outer circumferential part of the mounting frame for the imaging optical element of the passage type is the shortest, located between the first imaging lens 6 and the first reflecting mirror 7.

In addition, the structure has such a configuration that in the sub-scan plane, the optical axis 82 of the second imaging lens 8 does not coincide with the center line 81 of the mounting frame of the imaging optical element of the pass type.

In addition, the structure has such a configuration that the center line 81 of the mounting frame of the imaging optical element of the through type is located on the side of the center line (main beam) of the light beam incident on the second imaging lens 8, which is removed from the reflected light path 15.

Other structures and optical functions are similar to the first embodiment, and based on this, similar technical effects are achievable.

More specifically, in this embodiment, the second imaging lens 8, the distance between the light path 15 reflected by the first reflecting mirror 7, and the outer circumference of the mounting frame for the imaging optical element of the pass type is the shortest, located between the first imaging lens 6 and the first reflecting mirror 7.

The second imaging lens 8 has optical power in the sub-scanning direction, and it is a lens that is optically closest to the scanning surface 11.

In addition, this embodiment is designed so that in the sub-scanning plane, the optical axis 82 of the second imaging lens 8 does not coincide with the center line 81 of the mounting frame of the imaging optical element of the passage type.

In addition, this embodiment is designed so that the center line 81 of the contour of the mounting frame for the imaging optical element of the pass type is located on the side of the main beam of the light beam incident on the second imaging lens 8, which is removed from the path 15 of the reflected light.

Tables 4, 5 and 6 below show the technical characteristics of an optical scanning device according to a seventh embodiment of the present invention.

Table 4 Surface R D N Light source 1 one 30.28 1,000 Condenser Lens 2 2 46.63203 1.00 1,785 3 15,51899 2.00 1,582 four -21,487 6.00 1,000 Aperture 3 5 endless 5.92 1,000 Cylindrical lens 4 6 aspherical (described below) 7.00 1,511 7 endless 83.90 1,000 Deflecting surface 5 8 endless 31.00 1,000 1st imaging lens 6 9 aspherical (described below) 8.50 1,524 10 aspherical (described below) 60.00 1,000 2nd imaging lens 8 eleven aspherical (described below) 5.50 1,524 12 aspherical (described below) 95.00 1,000 Safety glass 10 13 endless 1.80 1,511 fourteen endless 68.70 1,000 Surface 11 scan fifteen endless

Table 5 Aspherical shape 6th surface 9th surface 10th surface 11th surface 12th surface Meridional form R endless -6.12E + 01 -4.06E + 01 -1.13E + 03 2.23E + 03 K 0 -3.84E + 00 -1.20E + 00 0 -1.07E + 04 B4 0 1.93E-07 5.08 E-08 0 -2.51E-07 B6 0 2.97E-10 3,52E-10 0 1,60E-11 B8 0 1,14E-13 -3.66-13 0 -6.08E-16 B10 0 9.88E-17 1,58E-16 0 5.26E-21 Sagittal form r 44.88 -1.00E + 03 1.00E + 03 -1.00E + 03 -3.17 E + 01 D2 0 0 0 0 6.34E-05 D4 0 0 0 0 -7.81E-09 D6 0 0 0 0 6.08E-13 D8 0 0 0 0 -3,15E-17 D10 0 0 0 0 5.17E-22

The circumscribed circle of the polygonal mirror = φ40.

The number of deflecting surfaces of the polygonal mirror = 6.

The angle defined between the optical axes of the input optical system and the optical imaging system = 70 degrees.

The reflecting point of a polygonal mirror, corresponding to the light beam of the center of the image, relative to the center (0,0) of the polygonal mirror = (15.05, 8.71).

The distance between the center of the polygonal mirror and the first reflecting mirror = 152.

The angle of incidence, determined between the normal to the first reflecting mirror and the incident light beam = 7.1 degrees.

Table 6 Fθm 226.2 Fθs 62.1 G1m 202.3 G1s -952.86 G2m -1431.8 G2s 62,4 TC 266.5 φa11 0.01609 φ1 -0.001 φ2 0.01602 φ1 / φa11 -0.0652 | 1 / r1 | + | 1 / r2 | 2,0E-03

The expressions in the present embodiment are similar to the expressions in the aforementioned first embodiment. In addition, the parameter definitions for the various components in the tables are similar to those for the first embodiment.

The optical function of the image forming system LB, which consists of the first and second image forming lenses 6 and 8 in the present embodiment, is explained below.

The first and second imaging lenses 6 and 8 are made of resin (plastic).

The optical imaging system LB is designed to image a light beam when scanning deflected by the optical deflector 5, and to form a point beam (spot) on the scanning surface 11 in order to scan the scanning surface 11 at a constant speed.

The imaging lens made of resin can be manufactured using the known molding technique by filling the mold with resin and removing it from the mold after cooling.

Thus, an imaging lens can be more easily fabricated compared to a conventional imaging lens based on a glass lens.

As shown in Table 2, the first imaging lens 6, having optical power predominantly in the main scanning direction, has an aspherical surface geometry, with a lens shape expressed by a function of the above equation.

The first imaging lens 6 has a higher optical power in the main scanning direction than its optical power in the sub-scanning direction. It also consists of a lens (meniscus lens) having non-arch geometry in the plane of the main scan and having a concave surface facing the side of the optical deflector 5.

In addition, the geometry of the first imaging lens 6 in the plane of the main scan is symmetrical about the optical axis.

Although with respect to the sub-scanning direction, the light entrance surface and the light exit surface have the same curvature and do not have optical power, the lens may have a cylindrical shape, for example, with both surfaces being flat in the sub-scanning direction.

For a light beam incident on it, the lens provides an imaging function primarily in the main scanning direction.

On the other hand, the second imaging lens 8 is an anamorphic lens having optical power mainly in the sub-scanning direction, as shown in Table 2. The shape of the lens corresponds to the geometry of the aspherical surface expressed by the function of the above equation.

The second imaging lens 8 in the sub-scanning direction has a higher optical power than its optical power in the main scanning direction. Also, the light entrance surface in the main scanning plane has an arc-shaped geometry, while the other surface has a non-arc-shaped geometry.

The geometry in the plane of the main scan is symmetric about the optical axis and does not have optical power in the direction of the main scan on the axis.

Regarding the geometry in the sub-scan plane, the light exit surface is a flat surface having very weak curvature, while the light exit surface has a convex shape in which the curvature changes gradually from the optical axis to the outside of the optical axis, and the geometry is symmetrical with respect to the optical axis.

For a light beam incident on it, this lens has an imaging function in the sub-scanning direction and a function of minor distortion correction in the main scanning direction.

With regard to the relationship of image formation in the sub-scanning direction of the image forming system LB, which consists of the first and second image forming lenses 6 and 8, what can be called a surface tilt correction system in which the deflecting surface 51 and the scanning surface 7 are in conjugate relationship.

It should be noted that the optical imaging system LB should not always be the functional expression shown in Table 2, but may be a known expression.

In addition, it may have asymmetric geometry with respect to the optical axis for further improved image forming performance.

In this embodiment (FIG. 9), after the scanning light beam 14, when scanned, is deflected by the deflecting surface 51, passes through the first imaging lens 6 and then the second imaging lens 8, it is reflected by the first reflecting mirror 7.

The center line 81 (Fig. 9) defines the contour of the mounting frame (not shown) for the imaging optical element of the pass-through type, the optical axis 82 is the axis of the imaging system LB.

In this embodiment, within the sub-scanning plane, the second imaging lens 8 is positioned so that the center line 81 of the fastener frame of the imaging optical element of the pass type is located on the side of the main beam of the light beam incident on the second imaging lens 8, which is remote from 15 paths of reflected light.

In this embodiment, by shifting the second imaging lens 8 in a direction perpendicular to the scanning light beam 14 only by a distance (shift amount) dZ, interference between the reflected light path 15 and the second imaging lens 8 is excluded.

Based on this, a reflection angle θ can be made small in the first reflection mirror 7, and this contributes to a decrease in the height of the device in the sub-scanning direction.

It should be noted that, as shown in Table 2, the radius of curvature of the second imaging lens 8 in the sub-scanning direction is 1000, and this lens is designed so that the optical axis 82 connecting the vertices does not coincide with the center line 81 of the path.

In the present embodiment, as shown in Table 2, the angle θ defined between the normal to the first reflecting mirror 7 as an optical element of the reflective type and the main beam of the scanning light beam 14 is

θ = 7.1 degrees.

This satisfies expression (3) as well as expression (4).

In addition, in this embodiment, the height H of the contour of the mounting frame of the imaging optical element of the passage type, which holds the second imaging lens 8, and the distance dZ from the center line 81 of the contour to the main beam of the incident light beam (scanning light beam) 14 are: H = 12.0 and dZ = 1.7. Thus, dZ / H = 0.142.

This satisfies expression (5), as well as conditional expression (6).

In the present embodiment, as can be seen from FIG. 9, the height of the device in the sub-scanning direction can be reduced by making the angle θ small.

The second imaging lens 8 should be offset in a direction perpendicular to the scanning light beam 14 to avoid interference between the reflected light path 15 and the second imaging lens 8.

Although the effect of decreasing the height can be enhanced if the shift amount dZ is performed larger, the largest possible shift amount is 1/2 of the lens height H, and this determines the upper limit for expression (5).

In addition, in a resin lens that is molded using a mold, if the height of the lens is small compared to the thickness of the lens in the direction of the optical axis, the cooling process develops immediately after the lens is released from the mold from the upper and lower parts of the lens.

As a result, the distribution of the refractive index and the distribution of birefringence are easily formed inside the lens within the sub-scan plane (direction along the height of the lens).

It is known that this effect becomes more significant if the distance from the central axis of the lens contour becomes larger and that the image forming performance deteriorates sharply from about two thirds (2/3) of the gap from the center of the contour to the outer outer edge.

Therefore, if the priority is the performance characteristic of the imaging device, the ratio should preferably satisfy dZ / H <0.3.

The upper limit of expression (6) defines this.

The lower limit of expressions (5) and (6) sets the lower limit of the shift value of the second imaging lens 8.

If the shift amount is small, the interference prevention effect for interference between the reflected light path 15 and the second imaging lens 8 becomes insufficient, and interference will occur if the position of the reflected light path 15 or the position of the second imaging lens 8 changes due to a tolerance build time. In this embodiment, the second imaging lens 8 having optical power in the sub-scanning direction is configured so that the center line 81 of the contour and the optical axis 82 are mutually offset by the physical distance dZ, although the main beam of the scanning light beam 14 and the optical axis 82 coincide with a friend. With this configuration, interference between the reflected light path 15 and the second imaging lens 8 is prevented, although, on the other hand, by ensuring that the main beam of the scanning light beam 14 and the optical axis 82 coincide, the deterioration of aberration and the occurrence of bending of the scanning path are reduced.

It should be noted that the principle of any one of the second to sixth embodiments may be included in the second imaging lens 8 of the present embodiment.

In addition, although the reflective mirror as a reflective type optical element used in the first to sixth embodiments is a planar mirror having no optical power, it may be a mirror with a curved surface.

A mirror with a curved surface, which is a reflective mirror, can have optical power either in the main scanning direction or in the sub-scanning direction.

An embodiment of an image forming apparatus

10 shows a schematic view and a sectional view, in a sub-scanning direction, of a main part of an image forming apparatus 104.

The image forming apparatus 104 receives the Dc code data supplied to it from an external computing device 117, such as a personal computer, for example. The code data Dc is then converted by the controller 111 of the printing device in the device into image-related data (raster dot data) Di.

The image related data Di is then input to the optical scanning unit 100 (optical scanning device), the configuration of which is set in accordance with any of the previous embodiments described above. The optical scanning unit 100 generates a light beam 103, which has been modulated in accordance with the image related data, Di, and with this light beam 103, the photosensitive surface of the photosensitive drum 101 is scanned in the main scanning direction.

The photosensitive drum 101, which is an electrostatic latent image bearing member (photosensitive member), rotates clockwise by a motor 115. When rotated, the photosensitive surface of the photosensitive drum 101 moves relative to the light beam 103 in a sub-scanning direction that is orthogonal to the main scanning direction .

Directly above the photosensitive drum 101 is a charging roller 102, which is in contact with the photosensitive surface of the drum to uniformly electrically charge the surface of the drum. A light beam 103 is projected onto the surface of the photosensitive drum 101, which has been electrically charged by the charging roller 102, scanned by the optical scanning unit 100.

As described above, the light beam 103 has been modulated in accordance with the image related data Di. By illuminating the photosensitive drum 101 with this light beam 103, an electrostatic latent image is formed on the surface of the photosensitive drum 101. The electrostatic latent image thus formed is then developed into a toner image with a developing device 107, which is located at a position lower from the irradiation position of the light beam 103 in relative to the rotational direction of the photosensitive drum 101 and which is in contact with the photosensitive drum m 101.

The toner image thus developed by the developing device 107 is transferred onto the image transfer sheet 112 (image transferring material) below the photosensitive drum 101 by the transfer roller 108, which is located opposite to the photosensitive drum 101.

The image transfer sheets 112 are stored in a cassette 109 of sheets in front (on the right side, as seen in FIG. 10) of the photosensitive drum, but they can be fed manually. There is a sheet feeding roller 110 at the end of the transfer sheet cassette 109 for feeding each sheet 112 from the cassette 109 to the sheet feeding guide.

A sheet of paper 112 with the presence of an unsecured toner image transferred to it as described above is transferred to the fixing device behind (on the left side, as seen in FIG. 10) of the photosensitive drum 101. The fixing device includes a fixing roller 113 with an integrated fixing heater (not shown) and a pinch roller 114 positioned to come into contact under pressure with the pinch roller 113. The image transfer sheet 112 supplied from the image transfer station is heated under pressure in the area of the pressure contact between the fixing roller 113 and the pressure roller 114, whereby the loose toner image on the transfer sheet 112 is fixed.

Behind the fixing roller 113, there are sheet unloading rollers 116 that act to unload the fixed image sheet 112 from the image forming apparatus.

Although not shown in FIG. 10, the printer controller 111 has various functions in addition to the data conversion function described above, for example, the engine control function 115 or any other components inside the image forming apparatus, as well as the polygon mirror engine inside the optical scanning unit (which will described later).

There is no particular limitation on the recording density of the image forming apparatus to be used in the present invention. However, since the higher the recording density, the higher the required image quality is, the structures according to the first and second embodiment of the present invention will be more effective when they are introduced into the image forming apparatus with a resolution of 1200 dpi or higher.

An embodiment of a color image forming apparatus

11 is a diagram of a main part of a color image forming apparatus according to an embodiment of the present invention. This embodiment is directed to a composite type of color image forming apparatus in which there are four optical scanning devices to record image related data on the surfaces of respective photosensitive drums (image bearing members) in parallel with each other.

The color image forming apparatus 60 (FIG. 11) comprises optical scanning devices 62, 63, 64 having a structure in accordance with any of the preceding embodiments, photosensitive drums 71, 72, 73 and 74 (image bearing elements), and developing devices 31, 32, 33 and 34, respectively, and the transport tape 51.

Although not shown in FIG. 11, the image forming apparatus further comprises an image transfer apparatus for transferring the toner image developed by the developing device to the image transfer material, and a fixing device for fixing the transferred toner image to the transfer sheet.

A color image forming apparatus 60 that receives color signals R (red), G (green) and B (blue) supplied to it from an external computing device 52, for example a personal computer. These color signals are converted by the printer controller 53 inside the image forming apparatus into image-related data (raster dot data) corresponding to C (cyan), M (magenta), Y (yellow) and B (black).

These image-related data are input to optical scanning devices 61, 62, 63 and 64, respectively. In response, these optical scanning devices emit light beams 41, 42, 43 and 44 that have been modulated in accordance with the associated image data. Through these light beams, the photosensitive surfaces of the photosensitive drums 71, 72, 73 and 74 are scanned in the main scanning direction.

In the color imaging apparatus of this embodiment, there are four optical scanning devices 61, 62, 63 and 64, and they correspond to colors C (cyan), M (magenta), Y (yellow) and B (black), respectively. These scanning devices act in parallel to each other to record image-related signals on the surface of the photosensitive drums 71, 72, 73 and 74, respectively, so that the color image can be printed at high speed.

As described, the color image forming apparatus of this embodiment uses four optical scanning devices 61, 62, 63 and 64 to create latent images for different colors on the surfaces of the respective photosensitive drums 71, 72, 73 and 74, respectively, using light beams based on relevant image data. After this, the images are superimposed onto the recording sheet, whereby a single full-color image is created on it.

As for the external computing device 52, for example, a color image reader with a sensor based on a charge coupled device (PES, CCD) can be used. In this case, the color image reader and the color image forming apparatus 60 will provide a color digital photocopier.

The invention has been described with reference to the structures disclosed herein, it is not limited to the details set forth, and it is intended that this application covers such modifications or changes that may fall within the scope of the improvement or scope of the appended claims.

Claims (14)

1. The optical scanning device containing
an optical deflector configured during scanning to deflect the light beam emitted from the optical radiation source means,
an optical imaging system configured to image on the scanning surface of the light beam when scanning an optical deflector deflected by the deflecting surface;
the light beam incident on the deflecting surface of the optical deflector falls perpendicular to the deflecting surface in the sub-scan plane, the light beam incident on the deflecting surface of the optical deflector falls at an angle with respect to the optical axis of the optical imaging system in the plane of the main scan, along the light path between the optical deflector and the scanning surface are placed an image-forming optical element of a passage type, with which includes an optical imaging system and an optical element of a reflective type, which are arranged in the indicated order from the optical deflector, and in the sub-scanning plane, the angle θ between the main beam of the light beam reflected by the optical element of the reflective type and the normal to the optical element of the reflective type satisfies the condition θ≤ 45 °
in this case, in the sub-scanning plane, the image-forming optical element of the through type is located so as to avoid interference with the transmission of light reflected by the optical element of the reflective type, the central line of the image-forming optical element of the through type is positioned on one side of the main beam of the light beam incident on the image forming optical element of a passage type, which is remote from the path of light reflected by the optical element of the reflector type. 2. The device according to claim 1, characterized in that in the sub-scan plane, the angle θ defined between the main beam of the light beam reflected by the optical element of the reflective type and the normal to the optical element of the reflective type satisfies the condition θ≤30 °. 3. The device according to claim 1, characterized in that the optical power φ _{i of} the imaging optical element of the through type in the sub-scan plane and the optical power φ _{all of the} optical imaging system in the sub-scan plane satisfy the condition | φ _i / φ _all | ≤0.01 . 4. The device according to claim 1, characterized in that the radius R1 (mm) of curvature in the direction of scanning the surface of the light input of the image-forming optical element of the passage type and the radius R2 (mm) of curvature in the direction of scanning the surface of the light exit of the image-forming optical element of the passage type satisfy condition | 1 / R1 | + | 1 / R2 | <0.0067 (1 / mm). 5. The device according to claim 1, characterized in that in the sub-scan plane the optical axis of the image-forming optical element of the pass-through type does not coincide with the central contour line of the image-forming optical element of the pass-type, while in the subscan plane the main beam of the light beam incident on the image-forming an optical element of a through type, passes through the optical axis of an image forming optical element of a through type. 6. The device according to claim 1, characterized in that the imaging optical element of the passage type is made of resin material. 7. The device according to claim 1, characterized in that in the sub-scanning plane the height H (mm) of the external configuration of the mounting frame holding the image-forming optical element of the passage type, and the physical distance dZ (mm) from the center line of the contour to the main beam of the light beam, incident on the surface of the light entrance forming the image of the optical element of the passage type satisfy the condition 0.05 <dZ / H <0.5. 8. The device according to claim 1, characterized in that the imaging optical element of a through type has a base surface for positioning in the plane of the main scan, and the base surface is located outside the effective region of the optical surface of the imaging optical element of a through type. 9. The device according to claim 1, characterized in that the imaging optical element of a through type has a support protrusion for determining the base position in the plane of the main scan, which is located on the side of the light input surface corresponding to the imaging optical element of a through type. 10. The device according to claim 1, characterized in that in the sub-scan plane the imaging optical element of the through type has a concave-shaped support element for determining the base position in the main scanning plane, which is placed on the outer circumferential part of the imaging optical element of the through type in the sub-scanning direction . 11. The device according to claim 1, characterized in that in the sub-scan plane, the end surface on the outer circumferential part of the mounting frame in the sub-scan direction for holding the imaging optical element of the through type has a cone-shaped geometry (shape) along the light path reflected by the reflective optical element . 12. The optical scanning device according to any one of claims 1 to 11, characterized in that it contains
two optical imaging systems located in the sub-scan plane, between which an optical deflector is placed. 13. An image forming apparatus comprising
an optical scanning device according to any one of claims 1 to 12;
a photosensitive element located near the scanning surface,
a developing device configured to develop into the toner image an electrostatic latent image formed on the photosensitive member by a light beam scanned by the optical scanning device;
an image transfer device configured to transfer the developed toner image to the transfer material; and
a fixing device configured to secure the transferred toner image to the transfer material. 14. An image forming apparatus comprising
an optical scanning device according to any one of claims 1 to 12; and
a printer controller configured to convert the encoded data input into it from the external device into an image-related signal and input the image-related signal into an optical scanning device.

Images